Chun Du

A Planar Copolymer for High Efficiency Polymer Solar Cells

An alternating copolymer, poly(2-(5-(5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo[c][1,2,5]thiadiazol-7-yl)thiophen-2-yl)-9-octyl-9H-carbazole) (HXS-1), was designed, synthesized, and used as the donor material for high efficiency polymer solar cells. The close packing of the polymer chains in the solid state was confirmed by XRD. A J(sc) of 9.6 mA/cm(2), a V(oc) of 0.81 V, an FF of 0.69, and a PCE of 5.4% were achieved with HXS-1 and [6,6]-phenyl C(71)-butyric acid methyl ester (PC(71)BM) as a bulk heterojunction active layer spin-coated from a solvent mixture of 1,2-dichlorobenzene and 1,8-diodooctane (97.5:2.5) under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW/cm(2).

6,7-dialkoxy-2,3-diphenylquinoxaline based conjugated polymers for solar cells with high open-circuit voltage

Abstract6,7-Dialkoxy-2,3-diphenylquinoxaline based narrow band gap conjugated polymers, poly[2,7-(9-octyl-9H-carbazole)-alt-5,5-(5,8-di-2-thinenyl-(6,7-dialkoxy-2,3-diphenylquinoxaline))] (PCDTQ) and poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5,8-di-2-thinenyl-(6,7-dialkoxy-2,3-diphenylquinoxaline))] (PFDTQ), have been synthesized by Suzuki polycondensation. Their optical, electrochemical, transport and photovoltaic properties have been investigated in detail. Hole mobilities of PCDTQ and PFDTQ films spin coated from 1,2-dichlorobenzene (DCB) solutions are 1.0 × 10−4 and 4.1 × 10−4 cm2V−1 s−1, respectively. Polymer solar cells were fabricated with the as-synthesized polymers as the donor and PC61BM and PC71BM as the acceptor. Devices based on PCDTQ:PC71BM (1:3) and PFDTQ:PC71BM (1:3) fabricated from DCB solutions demonstrated a power conversion efficiency (PCE) of 2.5% with a Voc of 0.95 V and a PCE of 2.5% with a Voc of 0.98 V, respectively, indicating they are promising donor materials.

Conjugated polymers with 2,7-linked 3,6-difluorocarbazole as donor unit for high efficiency polymer solar cells

A novel donor–acceptor (D–A) copolymer PDFCDTBT with 3,6-difluoro substituted carbazole as the donor unit and dialkoxy substituted benzothiadiazole as the acceptor unit has been synthesized and used as a donor material for bulk heterojunction polymer solar cells (BHJ PSCs). PDFCDTBT possesses a band gap of 1.75 eV, a low-lying HOMO energy level of −5.23 eV, and a good thermal and electrochemical stability. In comparison with the corresponding non-fluoro substituted HXS-1, which has a HOMO energy level of 5.21 eV, a LUMO energy level of 3.35 eV, and an optical band gap of 1.86 eV, the incorporation of two fluoro atoms in the carbazole donor unit lowers the HOMO and the LUMO energy levels of the polymer, which results in simultaneously decreasing the band gap of the polymer and increasing the Voc of polymer solar cells. The fluoro-containing polymer PDFCDTBT also shows strong intramolecular interactions and forms close packing in the solid state. Polymer solar cells based on PDFCDTBT and (6,6)-phenyl-C71-butyric acid methyl ester (PC71BM) demonstrate a power conversion efficiency (PCE) of 4.8% with a Voc of 0.91 V, a Jsc of 9.5 mA cm−2, and an FF of 0.55. In comparison with HXS-1, the better stability, higher Voc, and narrower band gap indicate that PDFCDTBT is a very promising donor material for high efficiency polymer solar cells.

Synthesis of Shape‐Persistent Macrocycles by a One‐Pot Suzuki–Miyaura Cross‐Coupling Reaction

Shape-persistent macrocycles have attracted considerable interest as molecular components in the fields of supramolecular chemistry and materials science due to their unique molecular structures and properties. These rigid molecular rings with a nanoscale sized hole in the center may be tailored with specific chemical constitutions, geometrical shapes, peripheral functional groups, and so on. Recent advances in the preparation, supramolecular self-assembling, and practical applications of shape-persistent macrocycles have verified this class of molecules as promising building blocks for supramolecular chemistry and nanodevice fabrication. Intense efforts have been devoted to the synthesis of shape-persistent macrocycles, and they have been well summarized in several excellent reviews. The most successful methods used in the synthesis of shape-persistent macrocycles include the following approaches: 1) intramolecular ring closure of a,w-difunctionalized oligomer strategy and the one-pot intermolecular coupling and intramolecular cyclization method; 2) the template strategy; 3) thermodynamically controlled synthetic strategies. Based on these elegant synthetic strategies, a large number of shape-persistent macrocycles with well-defined shapes and sizes have been prepared and reported. Recently, Sherburn and Sinclair found that Suzuki– Miyaura coupling of diiodoaryls and arylboronic acid in a feed ratio of 10:1 afforded the product of double coupling in good yields. Hu and Dong demonstrated that the use of [Pd2ACHTUNGTRENNUNG(dba)3] and tBu3P as the catalyst precursor for Suzuki– Miyaura cross-coupling of dibromobenzenes with arylboronic acid (1 equiv) afforded exclusively diaryl-substituted benzenes. Scherf et al. reported the cross-coupling of 2,7-dibromofluorene with arylboronic acid (1 equiv) formed preferentially the diaryl-substituted fluorenes. Yokozawa et al. reported chain-growth Suzuki–Miyaura polymerization of an AB-type monomer, bromoarylboronic acid, using [PdBr{P ACHTUNGTRENNUNG(tBu)3}(Ph)] as an arylpalladium halide catalyst. Kiriy et al. have successfully grafted polyfluorene onto a functionalized surface by catalyst-transfer chain-growth Suzuki–Miyaura polycondensation of 7-bromo-9,9-bis(2ethyl-hexyl)-9H-fluoren-2-ylboric using [Pd ACHTUNGTRENNUNG(tBu3P)2] as the catalyst precursor. Very recently, Yokozawa et al. have demonstrated that catalyst-transfer Suzuki–Miyaura polycondensation can be used to prepare even diblock conjugated polymers with a narrow molecular weight distribution. We have recently demonstrated that the catalyst-transfer Suzuki–Miyaura cross-coupling (CTSMCC) reaction can be used to prepare hyperbranched polymers with a branching degree of 100%. We think the unique catalyst-transfer behavior can be used to prepare shape-persistent macrocycles. Herein, we report the application of the CTSMCC reaction in the preparation of shape-persistent macrocycles. To the best of our knowledge, this is the first example of the synthesis of macrocycles by the CTSMCC reaction. Four macrocycles were selected as targeted macrocycles to verify our idea. Due to the competition of linear polymerization, a onepot reaction usually affords macrocycles in very low yield. Therefore, the synthesis of shape-persistent macrocycles normally requires pseudo high dilution. The reactants are usually added to the reaction vessel by a syringe pump over [a] W. Huang, M. Wang, C. Du, Dr. Y. Chen, L. Su, C. Zhang, Prof. Dr. Z. Bo Institute of Chemistry CAS Beijing 100190 (P.R. China) Fax: (+86)10-82618587 E-mail : zsbo@iccas.ac.cn [b] Dr. R. Qin, Prof. Dr. Z. Liu, C. Li, Prof. Dr. Z. Bo Institute of Polymer Chemistry and Physics College of Chemistry, Beijing Normal University Beijing 100875 (P.R. China) Fax: (+86)10-62206891 E-mail : zsbo@bnu.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201002574.

Polymer Photovoltaic Cells Based on Polymethacrylate Bearing Semiconducting Side Chains.

Polymethacrylate with semiconducting side chains (P1), synthesized by free radical polymerization, was used as a donor material for polymer solar cells. P1 is of high molecular weight (Mn = 82 kg mol(-1)), good thermal stability, narrow band gap (1.87 eV), and low-lying HOMO energy level (-5.24 eV). P1 possesses not only the good film-forming ability of polymers but also the high purity of small organic molecules. Power conversion efficiencies (PCEs) of 0.63% and 1.22% have been obtained for solar cells with M1:PC71BM and P1:PC71BM as the active layers, respectively. With PC61BM as the acceptor, PCEs of M1 and P1 based devices decrease to 0.61% and 0.76%, respectively. To the best of our knowledge, this is the first report that free radical polymerization can be used to prepare polymer donors for photovoltaic applications.